Since a cellulosic ester resin (CA) film has transparency, optical isotropy, toughness, and favorable adhesiveness to polyvinyl alcohol (hereinafter abbreviated as “PVA”) which is a material for a polarizer for a liquid crystal display device, the CA film has been used as a polarizer-protecting film which constitutes a polarizing-plate for a liquid crystal display device such as a television or a laptop computer.
These polarizer protective films are required to have various properties, specifically, transparency, water vapor permeability resistance, dimensional stability against heat, and the like and, in recent years, there has been a demand for polarizer protective films which are excellent in these various physical properties. In addition, in recent years, liquid crystal display devices have been made thinner and polarizer protective films have also been thinned accordingly, and there is also a demand for the polarizer protective films to realize the above properties at a level of the related art or exceeding the level with a thinner film thickness.
In order to develop the various properties described above, for example, various modifiers such as triphenyl phosphate and ester compounds are added to cellulosic ester resins to produce cellulosic ester films. Then, in addition to developing the various properties described above, there is also a demand for the modifier to have a property (a volatilization-resistant property) of being less likely to cause contamination of the production line due to volatilization at the time of cellulosic ester film production.
For example, a polyester obtained by blocking the terminal hydroxyl group of a polyester polyol obtained using phthalic acid and propylene glycol with benzoic acid or paratoluic acid is known as a modifier which is able to provide a film excellent in water vapor permeability resistance and less likely causes contamination of the production line due to volatilization at the time of production (refer to, for example, PTL 1). However, there are problems in that the polyester disclosed in PTL 1 has insufficient compatibility with the cellulosic ester resin and the film becomes opaque when exposed to high-humidity and high-temperature environments.